“Age cannot wither her, nor custom stale her infinite variety.” That famous line from Antony and Cleopatra – uttered by Enobarbus in praise of Egypt’s queen – springs instantly to mind about Dame Judi Dench, who turned 80 in 2014.

While it’s easy enough to play the sycophant when a living legend hits a landmark birthday, the fact is that it’s true – there’s something about the greatest actress of our age that seems to resist the obvious ravages of time.

The force of her personality, the undimmed blaze of her intelligence, overrides the distractions of wrinkles, and the usual sorry sideeffects of getting on, while her mercurial properties, so abundant in every performance, mean that her work doesn’t exactly “date”.

The footage, especially of those popular sitcoms As Time Goes By and A Fine Romance, may get grainy but the raw material is durable. Watch her in the 1991 BBC recording of Absolute Hell, in which she supplied a tour de force as a quietly stricken club hostess in Forties Soho and it’s as searing as her portrayal of an ordinary woman coming to the end of a 50-year wait to find out what became of her forcibly adopted son – last year’s hit Philomena. “Energy I have,” she recently told an interviewer, with pride – she’s still working, and hard.

Judi Dench in Casino Royale

She’s currently filming Richard III with Benedict Cumberbatch – playing the Duchess of York – has completed a sequel to The Best Exotic Marigold Hotel and sees in the New Year starring opposite Dustin Hoffman as a woman obsessed with her tortoise in a BBC adaptation of a Roald Dahl book, Esio Trot.

You might suppose she’s somehow making up for lost time; it took a while for the worlds of television and film to cotton on to just how good she is. Hollywood didn’t sit up and take note until she got cast as M in the Bond film Goldeneye in 1995 – a role she made as complex and interesting as anything in the franchise, culminating in a climactic turn in Skyfall that stole the show.

Her subsequent Oscar-nominated performance as Queen Victoria in Mrs Brown confirmed that she could reach out and touch millions on the big screen. Yet her reputation as the doyenne of stage actresses has long been so entrenched that she really has had nothing left to prove. She still does it because it’s in her bones. She set off in early youth to become a set designer but acting swiftly claimed her. It had to – and that’s tied up with a quality she brings to almost all of her roles. She has confessed to being very shy – acting was a vital outlet for her – but the shyness, the restraint, lingers and it creates a remarkable sense of enigma.

Judi Dench in The Importance of Being Earnest

You can talk at length about the fascinations of Dame Judi’s voice – its rasping, lived-in quality, so memorable on that standout Sondheim song Send in the Clowns. You can muse on the unconventional nature of her leading lady looks, so short and gamine that she was sometimes underestimated when she started out (“a calm, wise, little Juliet”, Kenneth Tynan said of her Juliet) and she could dismiss herself too: “I do hope you know what you’re up to, casting a menopausal dwarf,” she half-teased Peter Hall when he asked her to play Cleopatra at the National.

But it’s those almost-intangibles that define her – the qualities of understatement, dignity, integrity, humanity. At one end of the spectrum this lends itself perfectly to the regal – Elisabeth I, Titania and so on – but it also makes her earthbound, one of us, capable of being moved to sudden passion, and being surprised at it, as achingly vulnerable as any.

She can be impassive, implacable, frightening – witness her long-hallowed performance as Lady Macbeth at the RSC in 1976. She can suggest too the girl still abiding inside the older woman, literally so in Pinter’s A Kind of Alaska, in which she mesmerised audiences as the hapless Deborah, waking into adulthood after three decades in a coma. You could say that her legacy has been as astonishing and as modest as she is: to help introduce a naturalism in performance that we now take for granted.

Born in York 1934, her father a doctor, she came into an acting world still beset by snobbery and class hierarchies, and she took a broom to it. Though she takes the work seriously, what we love about her is that she doesn’t give herself airs and graces, not that many anyway.

An eccentric spirit prevails – there’s a twinkle in her eyes, a reputation for causing mischief in rehearsal rooms. “I don’t want to work with anyone who can’t laugh at themselves or make mistakes or look foolish,” she has said. If she isn’t putting her feet up much at the moment, I hope she does today. The years fly by – she has made them the richer for her presence.